1. Field of the Invention
The present invention relates to a coating line construction and use of same and, more particularly, to a coating line construction so adapted as to coat a coating substrate with a paint in the process of conveying the coating substrate and use thereof.
2. Description of Related Art
Automotive vehicle bodies as a coating substrate are coated with a paint while they are conveyed on a coating line. The automotive vehicle bodies are generally coated sequentially with an undercoating paint, an intercoating paint and an overcoating paint. An overcoat on the automotive vehicle bodies generally comprises a base coat and a clear or solid coat to be formed thereon. The base coat constituting the overcoat serves as a basic portion for determining a final hue of the coat of the automotive vehicle bodies, and paints for the base overcoat are much more abundant in kind than paints for clear or solid coats. Further, oil-base paints have recently started being replaced gradually by water-base paints in order to compete with the environmental problems which are recently gathering increasing attention.
When the coat on the automotive vehicle body is to be mended or corrected, the coat to be mended or corrected is sprayed with a paint manually by an operator. In this case, the paint is sprayed several times in such a limited quantity that the paint is atomized to an extremely fine extent to thereby form a predetermined film thickness on the coat to be mended. Hence, the manual spraying can realize a color of the paint in its original hue, whether the color is pale or dark.
However, when the automotive vehicle bodies are automatically assembled on a large scale, the manual spraying for correcting or mending the coat requires a long period of time so that this is extremely disadvantageous for large-scale production of automotive vehicle bodies.
A coating station of the coating line for coating the automotive vehicle bodies with a base coat generally has two stages disposed in series along the coating line and the two stages for base coating are provided with air-nozzle type coaters. In other words, the conventional base coating station is disposed so as to be capable of coating with two different kinds of paints.
Japanese Patent Laid-open (kokai) Publication No. 289,265/1987 discloses the technology in which a conveyor is so disposed as to convey automotive vehicle bodies back and forth and one stage is repeatedly employed, thereby allowing the automotive vehicle bodies to be coated with two different types of paints in the one stage.
However, it is to be noted that either of the disposition of the two stages for base coating or the repetitive use of one stage for base coating is to form a predetermined film thickness by coating twice. In this case, as a matter of course, the period of time for coating in each stage is set as short as possible in order to meet with demands for production on a large scale, so that the quantity of the paint to be sprayed from each of the air nozzles in each stage is set larger than required. This means that particles of the paint to be sprayed from the air nozzles become large in size. Hence, in some cases, the extent to which the paint is atomized is not appropriate and the original color of the paint cannot be achieved.